It is well known that for the color development of a silver halide photographic light-sensitive material, after exposure, an oxidized aromatic primary amine developing agent can be reacted with a dye forming coupler to obtain a color image.
It is also known that, for the color development of a silver halide color photographic material, an oxidized aromatic primary amine color developing agent can be reacted with a coupler to form a dye such as an indophenol, an indoaniline, an indamine, an azomethine, a phenoxazine, a phenazine, and the like, thus forming a color image. In this procedure, the subtractive color process is ordinarily used for color reproduction, and silver halide emulsions which are selectively sensitive to blue, green and red light, and yellow, magenta and cyan color image formers, which are respectively the complementary colors of blue, green and red, are employed. For example, a coupler of the acylacetanilide or benzoylmethane type is used for forming a yellow color image; a coupler of the pyrazolone, pyrazolobenzimidazole, cyanoacetophenone or indazolone type is generally used for forming a magenta color image; and a phenolic coupler, such as phenols and naphthols, is generally used for forming a cyan color image.
Color couplers must satisfy various requirements. For example, it is necessary that they have a good spectral property and provide a dye image having excellent stability to light, temperature, and humidity for a long period of time upon color development.
It is also required in a multilayer color photographic light-sensitive material that couplers are fixed in respective layers separated from each other in order to reduce color mixing and improve color reproduction. Many methods for rendering a coupler diffusion-resistant are known. One method is to introduce a long chain aliphatic group into a coupler molecule in order to prevent diffusion. Couplers according to such a method require a step of addition to an aqueous gelatin solution by solubilizing in alkali, or a step of dispersing in an aqueous gelatin solution by dissolving in a high boiling point organic solvent, since the couplers are immiscible with an aqueous gelatin solution. Such color couplers may cause crystal formation in a photographic emulsion. Furthermore, when using a high boiling point organic solvent, a large amount of gelatin must be employed since the high boiling point organic solvent makes an emulsion layer soft. Consequently, this increases the thickness of the material even though it is desirable to reduce the thickness of the emulsion layer.
Another method for rendering a coupler diffusion-resistant is to utilize a polymer coupler latex obtained by polymerization of a monomeric coupler. An example of a method of adding a polymer coupler in a latex form to a hydrophilic colloid composition is a method in which a latex prepared by an emulsion polymerization method is directly added to a gelatino silver halide emulsion and a method in which an oleophilic polymer coupler obtained by polymerizaton of a monomeric coupler is dispersed in a latex form in an aqueous gelatin solution. Some examples of the former emulsion polymerization methods include an emulsion polymerization method in an aqueous gelatin phase as described in U.S. Pat. No. 3,370,952 and an emulsion polymerization method in water as described in U.S. Pat. No. 4,080,211. An example of the latter method in which a lipophilic polymer coupler is dispersed in a latex form in gelatin is described in U.S. Pat. No. 3,451,820. The method of adding a polymer coupler in a latex form to a hydrophilic colloid composition has many advantages in comparison with other methods. For example, the deterioration of strength of the film formed is small, because the hydrophobic substance is in a latex form. Also, since the latex can contain coupler monomers in a high concentration, it is easy to incorporate couplers in a high concentration into a photographic emulsion, and the increase of viscosity is small. Furthermore, color mixing is prevented, since a polymer coupler is completely immobilized and the crystallization of couplers in the emulsion layer is small. In particular, when the polymer coupler latex prepared by an emulsion polymerization method is used, the step of adding the coupler to a coating solution can be simplified, since the use of a high boiling point organic solvent or an alkali is not necessary and a special dispersing method is not required. Moreover, the thickness of the layer can be reduced, since an organic solvent is not contained therein.
With respect to the addition of these polymer couplers in a latex form to a gelatino silver halide emulsion, there are described, for example, 4-equivalent magenta polymer coupler latexes and methods of preparation thereof in U.S. Pat. No. 4,080,211, British Pat. No. 1,247,688, and U.S. Pat. No. 3,451,820, copolymer latexes with a competing coupler in West German Pat. No. 2,725,591, and U.S. Pat. No. 3,926,436 and cyan polymer coupler latexes in U.S. Pat. No. 3,767,412.
However, these polymer coupler latexes have a number of problems which need to be eliminated, in addition to the many advantages described above. The problems include the following:
1. The absorption peak of the magenta dye is broadened, and thus the color reproducibility is inferior.
2. The rate of the coupling reaction is poor, and thus the density of dye formed is very low.
3. The light fastness of the magenta color image is very poor.
4. Undesirable fog is readily formed upon color development.
5. The fastness to humidity and heat of the color image is poor.
6. The solubility of the coupler monomer is low, and the polymerizability thereof is very poor.
More particularly, they have major disadvantages in color reproducibility, coupling reactivity, light fastness of magenta color image, stability of polymer coupler latex in a film during storage, and the polymerizability of the coupler monomer. With respect to the coupling reactivity, no improvement is obtained by using the 2-equivalent magenta polymer coupler latex described in West German Pat. No. 2,725,591 and U.S. Pat. No. 3,926,436. This suggests that there are great differences in photographic properties between conventional couplers and polymer couplers.